A harmonic damper is a device connected to the free end of the crankshaft of an internal combustion engine. It is needed in engines with long crankshafts, such as straight-8 engines. It is used on most engines to reduce torsional vibrations that can occure at certain speeds.
The damper consists of an inner hub attached to the end of the crankshaft. An round mass is attached to the hub by an elastic material. This become a spring-mass-damper system. By selection of the damping material and the size of the mass, the damper can be made to quiet the torsional vibrations. The overall appearance is that of a thick disk.